The present invention relates to a hydrogen absorbing alloy capable of absorbing-desorbing hydrogen, a method of manufacturing the same, and an alkali secondary battery comprising a negative electrode containing a hydrogen absorbing alloy.
Known hydrogen absorbing alloys include a TiFe system having mainly a CsCl type structure, a MmNi5 system (Mm representing a misch metal) having a CaCu type structure, and (Ti, Zr)(V, Mn)2 system having structures of a MgZn2 type, MgCu2 type or a MgNi2 type. Vigorous researches are being made by many researchers on the use of the TiFe system hydrogen absorbing alloy as a hydrogen storing material and on the use of the MmNi5 system hydrogen absorbing alloy and the (Ti, Zr)(V, Mn)2 system hydrogen absorbing alloy as a material of the negative electrode of a high capacity secondary battery.
The hydrogen storing material is applied to a heat pump and a fuel battery, and a TiFe system hydrogen absorbing alloy that permits maintaining the absorption-desorption cycle of hydrogen over a long period of time because of its excellent properties of being poisoned has been developed.
A nickel-cadmium secondary battery and a nickel-hydrogen secondary battery are known as high capacity secondary batteries. Particularly, the nickel-hydrogen secondary battery comprising a negative electrode containing a hydrogen absorbing alloy that permits absorbing-desorbing hydrogen is widely used as a small hermetic secondary battery excellent in compatibility to the environment in a power source of a portable electronic appliance.
However, in a nickel-hydrogen secondary battery comprising a negative electrode containing a hydrogen absorbing alloy of the MmNi5 system (Mm: misch metal) or the TiMn2 system, the hydrogen absorbing capacity of the hydrogen absorbing alloy is limited, making it difficult to further increase the hydrogen absorbing capacity.
Under the circumstances, hydrogen absorbing alloys of V-Ti system and Ti2Ni system have been developed. However, these hydrogen absorbing alloys, which vigorously react directly with hydrogen under high temperatures, are poor in reactivity with hydrogen under room temperature, with the result that it is difficult to achieve an initial activation.
An object of the present invention is to provide a hydrogen absorbing alloy having a capacity density per unit volume and a capacity density per unit weight higher than those of the MmNi5 system hydrogen absorbing alloy and the TiFe system hydrogen absorbing alloy that are widely put to a practical use nowadays and exhibiting an initial activation more satisfactory than that of the TiMn2 system hydrogen absorbing alloy.
Another object of the present invention is to provide a method of manufacturing a hydrogen absorbing alloy in which the above-noted properties are further improved.
A still another object of the present invention is to provide an alkali secondary battery exhibiting a high capacity, compared with the case where the secondary battery comprises a negative electrode containing the MmNi5 system hydrogen absorbing alloy, and excellent in the high rate charge-discharge characteristics, compared with the case where the secondary battery comprises a negative electrode containing the TiMn2 system hydrogen absorbing alloy.
According to a first aspect of the present invention, there is provided a hydrogen absorbing alloy represented by a general formula AMx, where A is at least one element selected from IA group, IIA group, IIB group, and IVB group of the periodic table, and M is at least one element selected from VB group, VIB group, VIIB group, VIIIB group, IB group, IIB group, IIIA group, IVA group and VA group of the periodic table, x meets the relationship of 2.7 less than x less than 3.8, and an average atomic radius r meets the relationship 1.36 xc3x85xe2x89xa6rxe2x89xa61.39 xc3x85.
According to a second aspect of the present invention, there is provided a method of manufacturing a hydrogen absorbing alloy, wherein an alloy represented by a general formula AMx, where A is at least one element selected from IA group, IIA group, IIIB group, and IVB group of the periodic table, and M is at least one element selected from VB group, VIB group, VIIB group, VIIIB group, IB group, IIB group, IIIA group, IVA group and VA group of the periodic table, x meets the relationship of 2.7 less than x less than 3.8, and an average atomic radius r meets the relationship 1.36 xc3x85xe2x89xa6rxe2x89xa61.39 xc3x85, is subjected to a heat treatment under vacuum or an inert gas atmosphere under temperatures not lower than 300xc2x0 C. and lower than the melting point of said alloy.
According to a third aspect of the present invention, there is provided a hydrogen absorbing alloy represented by a general formula AMx, where A is at least one element selected from IA group, IIA group, IIIB group, and IVB group of the periodic table, and M is at least one element selected from VB group, VIB group, VIIB group, VIIIB group, IB group, IIB group, IIIA group, IVA group and VA group of the periodic table, x meets the relationship of 2.7 less than x less than 3.8, an average atomic radius r meets the relationship 1.36 xc3x85xe2x89xa6rxe2x89xa61.39 xc3x85, and said x and said r meet the relationship 1.41xe2x89xa60.017x+rxe2x89xa61.45.
According to a fourth aspect of the present invention, there is provided a method of manufacturing a hydrogen absorbing alloy, wherein an alloy represented by a general formula AMx, where A is at least one element selected from IA group, IIA group, IIIB group, and IVB group of the periodic table, and M is at least one element selected from VB group, VIB group, VIIB group, VIIIB group, IB group, IIB group, IIIA group, IVA group and VA group of the periodic table, x meets the relationship of 2.7 less than x less than 3.8, an average atomic radius r meets the relationship 1.36 xc3x85xe2x89xa6rxe2x89xa61.39 xc3x85, and said x and r meet the relationship 1.41xe2x89xa60.017x+rxe2x89xa61.45, is subjected to a heat treatment under vacuum or an inert gas atmosphere under temperatures not lower than 300xc2x0 C. and lower than the melting point of said alloy.
According to a fifth aspect of the present invention, there is provided a hydrogen absorbing alloy represented by a general formula AMx, where A is at least one element selected from IA group, IIA group, IIIB group, and IVB group of the periodic table, and M is at least one element selected from VB group, VIB group, VIIB group, VIIIB group, IB group, IIB group, IIIA group, IVA group and VA group of the periodic table, x meets the relationship of 2.7 less than x less than 3.8, an average atomic radius r (xc3x85) and an equilibrium pressure Peq (atm) during the hydrogen absorption meet the relationships 1.36xe2x89xa6rxe2x89xa61.39 and 0.1xe2x89xa6Peqxe2x89xa63.5, respectively.
According to a sixth aspect of the present invention, there is provided a method of manufacturing a hydrogen absorbing alloy, wherein an alloy represented by a general formula AMx, where A is at least one element selected from IA group, IIA group, IIIB group, and IVB group of the periodic table, and M is at least one element selected from VB group, VIB group, VIIB group, VIIIB group, IB group, IIB group, IIIA group, IVA group and VA group of the periodic table, x meets the relationship of 2.7 less than x less than 3.8, an average atomic radius r (xc3x85) and an equilibrium pressure Peq (atm) during the hydrogen absorption meet the relationships 1.36xe2x89xa6rxe2x89xa61.39 and 0.1xe2x89xa6Peqxe2x89xa63.5, respectively, is subjected to a heat treatment under vacuum or an inert gas atmosphere and under temperatures not lower than 300xc2x0 C. and lower than the melting point of the alloy.
According to a seventh aspect of the present invention, there is provided an alkali secondary battery comprising a negative electrode containing a hydrogen absorbing alloy represented by a general formula AMx, where A is at least one element selected from IA group, IIA group, IIIB group, and IVB group of the periodic table, and M is at least one element selected from VB group, VIB group, VIIB group, VIIIB group, IB group, IIB group, IIIA group, IVA group and VA group of the periodic table, x meets the relationship of 2.7 less than x less than 3.8, and an average atomic radius r meets the relationship 1.36 xc3x85xe2x89xa6rxe2x89xa61.39 xc3x85.
According to an eighth aspect of the present invention, there is provided an alkali secondary battery comprising a negative electrode containing a hydrogen absorbing alloy represented by a general formula AMx, where A is at least one element selected from IA group, IIA group, IIIB group, and IVB group of the periodic table, and M is at least one element selected from VB group, VIB group, VIIB group, VIIIB group, IB group, IIB group, IIIA group, IVA group and VA group of the periodic table, x meets the relationship of 2.7 less than x less than 3.8, an average atomic radius r meets the relationship 1.36 xc3x85xe2x89xa6rxe2x89xa61.39 xc3x85, and said x and said r meet the relationship 1.41xe2x89xa60.017x+rxe2x89xa61.45.
Further, according to a ninth aspect of the present invention, there is provided an alkali secondary battery comprising a negative electrode containing a hydrogen absorbing alloy represented by a general formula AMx, where A is at least one element selected from IA group, IIA group, IIIB group, and IVB group of the periodic table, and M is at least one element selected from VB group, VIB group, VIIB group, VIIIB group, IB group, IIB group, IIIA group, IVA group and VA group of the periodic table, x meets the relationship of 2.7 less than x less than 3.8, and an average atomic radius r (xc3x85) and an equilibrium pressure Peq (atm) during the hydrogen absorption meet the relationships 1.36xe2x89xa6rxe2x89xa61.39 and 0.1xe2x89xa6Peqxe2x89xa63.5, respectively.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.